1. Field of Invention
The present invention relates generally to fluid dispensing utensils and, more particularly, to a fluid dispensing utensil which is adapted to prevent leakage.
2. Description of the Related Art
Fluid dispensing utensils are commonly used to deliver fluids such as ink, paint, adhesives, shoe polish, lotion, medicine, perfume, makeup, white out and food. In one type of fluid dispensing utensil, a relatively large volume of fluid is stored in a non-capillary container (or reservoir) where it is allowed to move freely. Pens which incorporate such a container, for example, are referred to as xe2x80x9cfree inkxe2x80x9d pens. That is, the ink in the reservoir is usually in a liquid state, and is free to move about as the writing utensil is moved. Fluid in these utensils is transferred from the container to the delivery end (often referred to as a tip or a nib) via a capillary conveying line. A slight vacuum (underpressure) relative to the atmosphere is maintained within the container which prevents fluid in the conveying line from escaping from the utensil until the tip is brought into contact with the surface onto which fluid is to be dispensed. At this point, the force of attraction of the surface and the capillary force of the space between the surface and portions of the tip which are not in direct contact with the surface will cause the fluid to flow from the tip to the surface. As fluid is dispensed, air enters the container in a controlled manner via a precisely sized air inlet that is formed in the container and ends within the fluid. The air replaces the fluid so as to maintain the vacuum at a relatively constant level.
One problem associated with these dispensing devices is leakage caused by air expansion within the container. Specifically, when the air within the container is heated it expands. This causes the vacuum within the container to subside and increases the vapor pressure on the fluid. The reduced vacuum and increased vapor pressure cause the utensil to leak through the tip when oriented in the delivery orientation, i.e. when facing at least partially downwardly.
In an attempt to reduce these types of leaks, some ink pens include an overflow chamber having a capillary storage that will absorb ink. Fountain pens, for example, include a capillary storage in the front section and sometimes under the nib. This storage has a capillarity that is strong enough to prevent leakage when the pen is held in the writing position, but not so strong that it will be filled during a normal writing operation. The capillary storage will not receive fluid when there is substantial air expansion within the container. As a result, these capillary storage systems have been unable to prevent leakage from free ink pens which hold a relatively large volume of ink and, ultimately, a relatively large volume of air. They have also been unable to prevent the leakage caused by relatively large amounts of air expansion in smaller containers.
The storage capacity of existing fountain pen systems which are able to prevent leakage during temperature fluctuations associated with normal use is less than 2.0 milliliters. The reasons for this limitation are as follows. The conveying tube, which transfers fluid via capillary action, must be large enough to produce the desired ink flow during writing. The capillary storage consists of capillaries that must be larger than those of the conveying line. Otherwise, the storage would normally be filled with ink and unable to store excess ink as needed. The storage must also create enough capillary force to hold the ink when the fountain pen is being held vertically. Such force (which is often referred to as xe2x80x9ccapillary heightxe2x80x9d) is inversely related to the size of the capillaries. Thus, in order to increase the volume of the storage, it is necessary to reduce the size of the capillaries. This is not possible, however, because the storage capillaries must be larger than those of the conveying line, which in turn must be large enough to insure proper ink flow. Accordingly, the volume of liquid that can be stored by the capillary storage is limited. This limits the amount of ink that can be stored in the reservoir.
Other pens include capillary storages configured such that the vast majority of the pores are smaller than the air inlet and are made of a material that is the same or substantially similar to that which forms the conveying line. As a result, the capillary storage will normally be completely filled with fluid and unable to receive additional fluid when air expands within the container. One proposed method of reducing this problem is to reduce the size of the air inlet. The proposed method has proven to be unsuccessful, however, due to manufacturing limitations which make it prohibitively difficult to produce sufficiently small air inlets. Another proposed method of reducing this problem is to increase the size of the storage capillaries. This method has also proven unsatisfactory because the increase in pore size decreases the capillary height of the capillaries and reduces the amount of fluid that can be stored therein when the pen is in the upright position. Thus, to optimize the performance of the conveying line and the storage capillaries, the pore sizes of the conveying line and storage capillaries are preferably carefully controlled.
Still other pens include capillary storages that consist of a series of radially extending fins which form capillaries therebetween. There are a number of disadvantages associated with the fin-type capillary storages. For example, air interferes with the flow of ink back to the reservoir. In addition, fin-type capillary storages take up a relatively large portion of the overall volume of the pen, thereby substantially reducing the amount of volume available for the ink reservoir.
Yet another problem is that the capillary storage swells as it absorbs the excess fluid. The swelling causes the capillary storage to push against the container wall, thereby restricting the air within the capillary storage from releasing freely into the atmosphere, through the surface areas where the storage member pushes against the container wall. The trapped air within the capillary storage, however, prevents the capillary storage from absorbing additional excess liquid. Thus, the swelling limits the capillary storage from absorbing to its full capacity.
The general object of the present invention is to provide a fluid dispensing utensil which obviates, for practical purposes, the aforementioned problems in the art. In particular, one object of the present invention is to provide a fluid dispensing utensil which is capable of storing a relatively large volume of fluid without leaking during periods of container air expansion. Another object of the present invention is to provide a fluid dispensing utensil which is relatively inexpensive and easy to manufacture. Yet another objective is to provide a combination of pore sizes in the conveying line and the capillary storage that will channel the flow of fluid to the tip, and not radially to the capillary storage. At the same time, it is important to maximize the flow rate of fluid through the conveying line, so that ample supply of fluid is available for writing.
In order to accomplish these and other objectives, the present fluid dispensing utensil includes a container, a capillary conveying line and a capillary storage in direct contact with the conveying line. The average capillarity of the storage is generally less than that of the conveying line, at least in the area of the opening between the container and the rest of the utensil. In addition, the lowest capillarity of the storage is substantially less than that of the conveying line. That is, the largest pore size in the storage is substantially greater than that of the conveying line. Furthermore, the greatest capillarity of the storage is preferably substantially equal to or less than the lowest capillarity of the conveying line. That is, the capillary storage preferably has very few or no pores smaller than the largest pore of the conveying line, but no pores so large that they cannot hold the height of liquid above the bottom of the reservoir. Due to these features, the vast majority of the capillary storage pores are normally free of fluid and will only store fluid during periods of air expansion in the fluid container. As air in the container contracts back to its original volume, fluid will be drawn out of the storage by the conveying line and returned to the container. The capillary conveying line may be configured such that some of capillaries in the conveying line are relatively small and transfer fluid, while others are relatively large and transfer air. This allows air and liquid to flow in parallel through the conveying line in opposite directions. In addition, the container may be configured such that air is only able to enter the container via the conveying line. Thus, the conveying line may be used to regulate the amount of air flowing into the container.
It should be noted that the descriptive term xe2x80x9ccapillarityxe2x80x9d has been used herein to indicate the height up to which a liquid ascends within a pore of a given diameter. The greater the height, the greater the capillarity. In general, small size pores have greater capillarity than the larger size pores. In other words, the term xe2x80x9ccapillarityxe2x80x9d is indicative of the attractive force between a liquid and a pore.
There are a number of advantages over prior fluid dispensing utensils associated with the present invention. The primary advantage of the present fluid dispensing utensil lies in the fact that it will reliably function under greater temperature fluctuations (and resulting air expansions) than utensils which are presently commercially available. This reliability will also extend to greater fluid storage volumes than commercially available utensils (10 ml or more). This improved reliability will also extend to outside pressure variations, such as those which occur when a utensil is on an airplane. As noted above, fluid saturates the capillary storage in many prior dispensing utensils. This eventually results in undesired leakage. Conversely, the capillary storage in the present invention is substantially emptied each time the air expansion within the container subsides, thereby preventing the aforementioned leakage caused by full storages. In addition, the use of the conveying line as the air inlet eliminates the need to form a very small air inlet in the fluid container. As it is much easier to manufacture capillary conveying lines with pores that are often as small as one one-thousandth of an inch than it is to form an air inlet of similar dimensions in a molded plastic container, a utensil in accordance with the present invention is less expensive to manufacture than prior utensils.
In one embodiment of the invention, the capillary conveying line extends to the bottom (or rearward) area of the container and is surrounded up to the bottom area by a tube. Fluid is unable to enter the conveying line when the utensil is in the dispensing orientation and the conveying line itself becomes the only source of fluid. Thus, this arrangement provides additional protection against leakage.
The conveying line and storage may also be in direct contact with one another. There are a number of advantages associated with this arrangement. For example, as the vacuum in the reservoir increases (due to a temperature decrease) and fluid begins to drain from the capillary storage, the capillaries in the conveying line will absorb essentially 100% of the fluid and return it to the reservoir. This would not occur there was a gap (and, therefore, air) between the storage and the conveying line. First, the conveying line capillaries could not help draw the fluid out of the storage, as they do when in direct contact with the storage. Also, the air would prevent the some of the fluid from entering the conveying line. Thus, after a few air expansion cycles, utensils with a gap will begin to leak.
The conveying line and the capillary storage may, in accordance with another embodiment of the invention, be integrally formed; in other words, a unitary conveying line and capillary storage may be formed. As a result, the conveying line and storage may be manufactured in a single processing step to further reduce manufacturing costs. In accordance with another advantageous aspect of the invention, an air passage is provided between the exterior surface of the capillary storage and the interior surface of the container. The air passage may be provided in a variety of ways. For example, at least a portion of the exterior surface of the capillary storage may be surrounded by a porous shroud. Alternatively, a substantially rigid element may be arranged between the exterior surface of the capillary storage and the interior surface of the container. Adequate space may also be provided by making the inner surface of the housing rough or irregular. On the storage side, one or more discontinuities may be formed in the exterior surface of the storage.
The air passage is especially useful when the capillary storage is formed from open cell polyurethane foam because certain solvents used in marker inks can cause this type of foam to swell.
Furthermore, capillary storage formed from open cell polyurethane, for example, swells when used with certain solvents. However, if the capillary storage swells to the point that the storage makes continuous contact with the interior surface of the housing, the flow of air from the storage to will be hampered. This can cause leakage when pressure builds within the pen because air will be trapped within the pores in the capillary storage that are needed for ink storage. Accordingly, the passage improves air flow within the pen and provides an additional measure of prevention against leakage. Another embodiment of the present invention employs fibers that are resistant to swelling caused by certain solvents. For example, polyolefins, which may be any of the polymers and copolymers of the ethylene, propylene, et al. families of hydrocarbons, such as polyethylene or polypropylene, may be used. That is, such fibers are resistant to swelling so that the air within the capillary storage is free to flow from the storage.
To further minimize air within the storage from being trapped, the fibers in the storage may be aligned along the length of the reservoir. That is, porous fibers of the storage are aligned parallel to conveying line. Accordingly, even if the capillary storage does swell, the porous fibers along the side edges are open to allow the air within the storage to flow out of the storage.
The above described and many other features and attendant advantages of the present invention will become apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.